My cow makes a screech moo sound, whats wrong with her?

Question

it often bellows through the night, it doesn't sound like the normal moo, but like it is constipated

Answer 1

She is in heat.  This will go on for about 3 days a month.

Answer 2

is it ," moooooeee heee hee hee!", mad cow disease. otherwise, linda is right.